The present invention relates to a process for producing a lower aliphatic carboxylic acid ester, comprising reacting a lower aliphatic carboxylic acid and a lower olefin in a gas phase in the presence of an acid catalyst.
More specifically, the present invention relates to a process for producing a lower aliphatic carboxylic acid ester with high efficiency, where a lower alcohol corresponding to a hydrate of the lower olefin is added to a reaction product containing a lower aliphatic carboxylic acid and a lower aliphatic carboxylic acid ester, obtained by reacting a lower aliphatic carboxylic acid and a lower olefin in a gas phase in the presence of an acid catalyst, to convert the lower aliphatic carboxylic acid in the reaction product into a lower aliphatic carboxylic acid ester and the lower aliphatic carboxylic acid ester is separated and recovered.
Lower aliphatic carboxylic acid esters are a useful chemical substance for use in various fields such as various industrial materials and solvents. In particular, ethyl acetate is widely used as an alternative organic solvent to the benzene- or toluene-based solvent and various production processes have been proposed therefor and implemented in industry.
The production process of the lower aliphatic carboxylic acid ester, particularly the production process of ethyl acetate can be classified, by taking notice of the starting material therefor, into (1) a method using acetaldehyde, (2) a method using ethanol and acetic acid and (3) a method using ethylene and acetic acid.
Specific examples of the method (1) using acetaldehyde include the method described in Japanese Unexamined Patent Publication No. 11-140016 (JP-A-11-140016). Specific examples of the method (2) using ethanol and acetic acid include the method described in Japanese Unexamined Patent Publication No. 57-130954 (JP-A-57-130954). According to these methods, ethyl acetate can be produced relatively in a high yield but the method (3) using ethylene and acetic acid is recently drawing an attention as a more effective method.
In particular, with respect to the process for producing a lower aliphatic carboxylic acid ester by gas phase esterification starting from a lower aliphatic carboxylic acid and a lower olefin, for example, a production process using a heteropolyacid and/or a salt thereof as a catalyst is disclosed in Japanese Unexamined Patent Publication No. 4-139148 (JP-A-4-139148), No. 4-139149 (JP-A-4-139149), No. 5-65248 (JP-A-5-65248), No. 6-9459 (JP-A-6-9459) and No. 9-118647 (JP-A-9-118647).
In these production processes of a lower aliphatic carboxylic acid ester, the reaction is performed in a gas phase and therefore, the starting lower aliphatic carboxylic acid must be introduced into a reactor in the form of a gas. Accordingly, in view of the effective use of energy necessary for vaporization, it is important to elevate the conversion of the vaporized lower aliphatic carboxylic acid. For this purpose, in the esterification reaction, use of a lower olefin in an amount equivalent to or greater than the lower aliphatic carboxylic acid is generally proposed with an attempt to elevate the conversion of the lower aliphatic carboxylic acid.
In this case, a process described, for example, in Japanese Unexamined Patent Publication No. 5-140036 (JP-A-5-140036) is generally used, where unreacted lower olefin fed in excess is separated from lower aliphatic carboxylic acid ester, lower aliphatic carboxylic acid or the like, using a lower aliphatic carboxylic acid as an absorber liquid and then recycled.
This method, more specifically, the method of using a lower olefin in an amount equivalent to or greater than a lower aliphatic carboxylic acid in the esterification reaction and thereby elevating the conversion of the lower aliphatic carboxylic acid can successfully reduce the energy cost necessary for the vaporization of the lower aliphatic carboxylic acid. However, accompanying the increase in the excess ratio of lower olefin, the recycled amount increases and the energy required therefor increases. That is, the excess ratio of lower olefin has an optimal range in view of the balance between these two starting materials and the proportion where the lower olefin can be used in excess has an upper limit.
Accordingly, only by the above-described method, the improvement in the conversion of lower aliphatic carboxylic acid is limited and in turn, the saving of energy cost necessary for the vaporization of lower aliphatic carboxylic acid is limited.
The object of the present invention is to improve, in the process for producing a lower aliphatic carboxylic acid ester by gas phase esterification reaction starting from a lower aliphatic carboxylic acid and a lower olefin, the conversion of lower aliphatic carboxylic acid, which is difficult to attain only by the method of using a lower olefin in excess to the lower aliphatic carboxylic acid, and thereby provide an efficient production process of a lower aliphatic carboxylic acid ester.
In order to attain the above-described object, the present inventors have made extensive investigations on the process as a whole in the process for producing a lower aliphatic carboxylic acid ester by gas phase esterification reaction starting from a lower aliphatic carboxylic acid and a lower olefin.
As a result, it has been found that when a lower alcohol corresponding to a hydrate of the lower olefin is added to a reaction product during, in the midst of or independently of the process of separating the lower aliphatic carboxylic acid ester from the reaction product containing a lower aliphatic carboxylic acid and a lower aliphatic carboxylic acid ester at the outlet of a reactor where the gas phase esterification reaction of a lower aliphatic carboxylic acid and a lower olefin is performed, and when the lower aliphatic carboxylic acid is condensed with the alcohol to convert into a lower aliphatic carboxylic acid ester and the lower aliphatic carboxylic acid ester is separated, the productivity of lower aliphatic carboxylic acid ester is improved. The present invention has been accomplished based on this finding.
More specifically, the present invention (I) is a process for producing lower aliphatic carboxylic acid ester, comprising reacting a lower aliphatic carboxylic acid and a lower olefin in a gas phase in the presence of an acid catalyst, wherein the production process comprises the following first and second steps:
First step:
a step of adding a lower alcohol corresponding to a hydrate of the lower olefin to the reaction product containing a lower aliphatic carboxylic acid after the gas phase reaction and thereby obtaining a reaction product having added thereto a lower alcohol; and
Second step:
a step of condensing the lower aliphatic carboxylic acid and the lower alcohol in the reaction product having added thereto a lower alcohol, obtained in the first step, and while allowing the conversion into a lower aliphatic carboxylic acid ester to proceed, separating the lower aliphatic carboxylic acid ester.
The present invention (II) is a process for producing a lower aliphatic carboxylic acid ester, comprising reacting a lower aliphatic carboxylic acid and a lower olefin in a gas phase in the presence of an acid catalyst, wherein the production process comprises the following first to third steps:
First step:
a step of adding the same lower aliphatic carboxylic acid as used in the above-described reaction to the reaction product containing a lower aliphatic carboxylic acid after the gas phase reaction and thereby obtaining a reaction product having added thereto a lower aliphatic carboxylic acid;
Second step:
a step of adding a lower alcohol corresponding to a hydrate of the lower olefin to the reaction product having added thereto a lower aliphatic carboxylic acid, obtained in the first step, and thereby obtaining a reaction product having added thereto a lower alcohol; and
Third step:
a step of condensing the lower aliphatic carboxylic acid and the lower alcohol in the reaction product having added thereto a lower alcohol, obtained in the second step, and while allowing the conversion into a lower aliphatic carboxylic acid ester to proceed, separating the lower aliphatic carboxylic acid ester.
The present invention (III) is a process for producing a lower aliphatic carboxylic acid ester, comprising reacting a lower aliphatic carboxylic acid and a lower olefin in a gas phase in the presence of an acid catalyst, wherein the production process comprises the following first to fourth steps:
First step:
a step of separating the reaction product after the gas phase reaction containing a lower aliphatic carboxylic acid and a lower aliphatic carboxylic acid ester into a moiety substantially containing a lower aliphatic carboxylic acid as the main component and a moiety substantially containing a lower aliphatic carboxylic acid ester as the main component;
Second step:
a step of adding a lower alcohol corresponding to a hydrate of the lower olefin to the moiety substantially containing a lower aliphatic carboxylic acid as the main component, obtained in the first step, and thereby obtaining a product having added thereto a lower alcohol;
Third step:
a step of condensing the lower aliphatic carboxylic acid and the lower alcohol contained in the product having added thereto a lower alcohol, obtained in the second step, to cause conversion into a lower aliphatic carboxylic acid ester; and
Fourth step:
a step of separating the lower aliphatic carboxylic acid ester obtained in the third step and thereby obtaining a lower aliphatic carboxylic acid ester.